This invention is related to seals for ball valves or spherical plug valves in which the seal rings are constructed generally in the form of a belleville spring. In this invention, the seal ring sealing surface engages the generally spherical surface of the valve ball member in substantially a line contact when the ball is in an undisplaced position. When the ball valve member is displaced downstream upon application of fluid pressure in a closed position the seal ring contacts the ball valve member along a substantially larger sealing surface.
One goal of valve manufacturing is to produce a valve which provides a fluid tight closure for high temperature applications. Unfortunately, prior art valve constructions for ball and spherical plug valves are not particularly well adapted for high temperature applications because they generally use elastomeric or plastic seals in their construction which deteriorate or fail upon application of elevated temperatures. Special compositions of material to resist high temperatures have been constructed to replace conventional elastomeric and plastic seals in ball valves. However, these are mere substitutes in material and do not vary the basic construction of the valve.
Another goal of valve manufacture is to provide a spherical plug valve which requires a low operating torque to rotate the valve member between the open and closed positions. The above described elastomeric and plastic seals usually require a considerable amount of torque to rotate the valve member because the valve seals are constructed with a relatively large contact area with the ball member and the seal rings must be preloaded to insure a fluid tight seal at low pressure and this high preloaded construction creates a great resistance to rotation of the ball member which is undesirable. Another disadvantage of the prior art valve constructions is that the seal rings generally do not scrape or clean the ball to any significant extent as it is rotated between the open and closed positions which allow foreign matter to accumulate on the ball and be moved under the seal rings thereby scratching and deforming them and this in turn increases the possibility of leakage.
Some spherical plug valves are known in the art which have been constructed with flexible seal rings suitable for high temperature operation. One of these valves is shown in U.S. Pat. No. 2,890,856 which shows a flexible metallic seal ring having peripheral edges thereof rigidly secured radially in the valve body and having a frusto-conical portion with an inner side thereof contacting the ball valve member. While this valve employs a metallic construction it has a relatively broad sealing surface which will not clean the ball and which will require large preloading forces for low pressure sealing.
Some spherical plug valves are known which have seals that form only a line contact with the ball valve member; one such valve is shown in U.S. Pat. No. 3,556,471. This valve employs a curved surface on a pivotally mounted elastomeric or plastic seal ring to seal aginst the ball valve member. While this valve does provide line contact between the seal ring and the ball valve member it is not suitable for high temperature and because it maintains line contact at all times the seal ring is very susceptible to crushing at high pressures.